The present invention relates to an air filter suitable for use in air cleaners, room air-conditioners, and particularly in car air-conditioners in which air is driven at a high speed.
For high efficiency dust collection and deodorization with a reduced pressure loss, it has been proposed to use a pleated paper-like dust-collecting and/or deodorizing filter. By virture of pleating, the filter can have an increased surface area of contact with air. The paper-like filter is formed from an electricified nonwoven fabric or an electricified sheet of fibers formed like a nonwoven fabric. The electricified sheet of fibers is known to collect submicron dust particles as well as larger particles due to a Coulomb's force imparted to the sheet of fibers through the electricification, and even an electricified sheet of fibers having a small mass per unit area is superior in the performance of dust collection to a nonwoven fabric not electricified.
For the conventional air filter used in car air-conditioners in which air is driven at a high speed, however, mechanical dust collection (by inertia and collision) is essential, rather than the Coulomb's force. Namely, the electrification will not lead to any efficient dust collection when an air filter having a Coulomb's force is used in such a car air-conditioner. In an air cleaner in which air is driven at a high speed, a high efficiency of dust collection can be attained by an air filter which has an ample and effective contact with dust particles. However, since a fibrous or paper-like air filter made using a nonwoven fabric or sheet of fibers as a matrix incurs a large pressure loss, an increase in surface area of the air filter by pleating will only lead to some reduction of the pressure loss. Imparting the function of deodorization to the air filter will additionally increase the pressure loss. Such air filters provide no effective and efficient dust collection and deodorization in applications for which the pressure loss should be small. Also since mechanical dust collection is more essential for collection of coarse dust particles of 5 .mu.m or more in size, the electricification of the matrix for the air filter did not allow any effective dust collection in applications in which air is to be driven at a high speed and coarse dust particles are to be collected.